Which rule outlines the requirement for a train not to enter a block unless it is clear?

The correct choice is associated with the principle of ensuring that a train does not enter a block unless it is completely clear of any obstructions or other trains. This requirement is vital for maintaining safety and preventing collisions on the tracks.

Rule 316 specifically addresses the conditions that must be met before a train can safely enter a block. This includes the necessity for the block to be unoccupied, which is crucial for the smooth operation of rail traffic and the safety of personnel and passengers. By mandating that a train only enter a clear block, the rule helps to establish a systematic approach to train movements, ensuring that the track ahead is safe for travel.

Other rules mentioned may cover different aspects of operation, such as procedures for signals, speed regulations, or emergency protocols, but Rule 316 is the specific guideline that deals with the occupational status of a block prior to train entry. This detail is crucial for both the safety of the train operations and the effective management of rail services.